Nucleic acid molecule encoding Ste20 oxidant stress response kinase-1 (SOK-1) polypeptide

ABSTRACT

A SOK polypeptide, an isolated DNA having a nucleotide sequence encoding a SOK polypeptide, and a method of determining whether a candidate compound modulates SOK-1 activity or expression, comprising the steps of providing a first and a second recombinant cell expressing a SOK gene; introducing a candidate compound into the first cell, but not into the second cell; measuring a SOK function in the first and second cells; and comparing the results obtained with the first and second SOK transformed cells, wherein an increase or decrease in the SOK function in the first cell compared to the second cell is an indication that the candidate compound modulates SOK expression or activity.

STATEMENT AS TO FEDERALLY SPONSORED RESEARCH

This invention was supported in part by U.S. Public Health Service Grants DK41513, GM46577, DK39773, DK38452 and NS10828, and an award from the NIDDK. The government may have certain rights in the invention.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a divisional application of U.S. Ser. No. 08/852,743, filed May 7, 1997 and issued as U.S. Pat. No. 5,830,699, which is a continuation in part of provisional application U.S. Ser. No. 60/016,774, filed May 7, 1996.

BACKGROUND OF THE INVENTION

The invention relates to protein kinases and methods of activating or inhibiting the expression of protein kinases.

Mitogen-activated protein kinase (MAPK) cascades have been remarkably conserved in evolution. The core of these cascades is a three-tiered module of serine/threonine kinases that consists of a MAPK-extracellular signal regulated kinase kinase (a MEKK), a MEK, and a MAPK or extracellular signal regulated kinase (ERK). In simple eukaryotes, such as the budding yeast Saccharomyces cerevisiae (S. cerevisiae), and the fission yeast, Saccharomyces pombe (S. pombe), these cascades are activated predominantly by cellular stresses such as nutritional starvation and osmolar stress (reviewed in Elion, TIBS 5:322 (1995); Herskowitz, Curr. Oper. Cell 80:187 (1995); and Levin et al., Cell Biol. 7:197 (1995)). In mammals, these cascades have evolved to allow responses to complex stimuli (e.g., growth factors and inflammatory cytokines), but in many cases, such as the response to osmolar challenge (Galcheva-Gargova et al., Science 265:806 (1994); Han et al., Science 265:808 (1994)), the primitive stress responses remain intact.

Epistasis analyses in yeast suggest that the Sterile 20 (Ste20) protein serine/threonine kinases and related protein kinases act upstream of the three tiered module. Three mammalian homologs of Ste20 have been reported to date: p21-activated protein kinase (PAK1) and related PAKs (Manser et al., Nature 367:40 (1994); Martin et al., EMBO J. 14:1970 (1995)); germinal center (GC) kinase (Katz et al., J. Biol. Chem. 269:16802 (1994)); and mammalian Ste20-like kinase 1 (MST1) (Creasy et al., J. Biol. Chem. 270:21695 (1995)). Mammalian Ste20s may function upstream of MEKK/MEK/MAP kinase pathways. PAK1 (Manser et al., Nature 367: 40 (1994)) and GC kinase (Katz et al., J. Biol. Chem. 269:16802 (1994)) have been shown to be capable of activating mammalian MAPK kinases (Polverino et al., J. Biol. Chem. 270:26067 (1995); Pombo et al., Nature 377:750 (1995); Zhou et al., J. Biol. Chem. 270:12665 (1995)), further illustrating remarkable evolutionary conservation of the MAPK kinases. When co-transfected with MAP kinase, both PAK1 and GC kinase activate the stress-activated protein kinase (SAPK)/c-Jun amino terminal kinase (JNK) cascade. PAK1 also activates the stress activated MAPK, p38, as well.

Ste20 protein kinases can be divided into two families based on their structure and regulation. The first family is the Ste20 family, which includes Ste20, PAK1 and related PAKs. These proteins contain a carboxy terminal catalytic domain and an amino terminal regulatory domain which has a p21^(cdc42/rac1) binding region (Manser et al., Nature 367:40 (1994); Martin et al., EMBO J. 14:1970 (1995)). PAK1 appears to be activated by binding to cdc42Hs or Rac1. Following binding to the small GTP-binding proteins, the kinase undergoes autophosphorylation and is activated. Physiologic activators of PAK1 have been identified, and include the chemoattractant peptide fMetLeuPhe, and Interleukin 1 (IL-1) (Zhou et al., J. Biol. Chem. 270:12665 (1995)).

The second family of Ste20s is the Sps1 family. Members of this group include Sps1, which is encoded by the S. cerevisiae sporulation specific 1 gene, which is necessary for spore formation in response to nutritional starvation; and the mammalian genes MST1 and GC kinase. The catalytic domain is amino terminal in these proteins, and the function of their carboxy terminal regions has not previously been known. These kinases do not contain an identifiable Rac/cdc42Hs binding domain in their non-catalytic regions. The regulation of this family of Ste20s is not well characterized. MST1 appears to be activated by dephosphorylation. Sps1 and its MAPK, Smk1 (Krisak et al., Genes & Development 8:2151 (1994)), are transcriptionally regulated, being expressed only at certain stages of the sporulation process, but it is not known if there are other modes of regulation of Sps1. Physiological activators of the Sps1 family of Ste20s have not been previously identified.

SUMMARY OF THE INVENTION

The invention is based on the discovery of a novel mammalian protein kinase, SOK-1, that belongs to the Sps1 family of Ste20 homologs. SOK-1 (Ste20 oxidant stress response kinase 1) is a protein kinase which is activated by oxidant stress (e.g., 0.5 mM H₂ O₂).

Accordingly, the invention features an isolated nucleic acid encoding a SOK polypeptide, particularly SOK-1. The naturally occurring SOK polypeptide can be from a mammal, such as a human, non human primate, e.g., baboons, monkeys and chimpanzees, goats, pigs, micro-pigs, guinea pigs, rabbits, rats and mice. This nucleic acid encodes an amino acid sequence with at least 50% (preferably at least 60%, more preferably at least 70%, more preferably at least 85%) identity to the amino acid sequence set forth in FIG. 1 (SEQ ID NO:2). The invention also features a substantially pure preparation of a SOK polypeptide. The SOK polypeptide preferably has an amino acid sequence with at least 50% sequence identity to the sequence set forth as SEQ ID NO:2. Preferably, the sequence has at least 60%, 70% or 85% sequence identity to the sequence set forth as SEQ ID NO:2. By "SOK polypeptide" is meant all or part of a novel protein kinase, expression of which is activated by oxidant stress.

By "isolated" is meant that the DNA is free of the coding sequences of those genes that, in the naturally-occurring genome of the organism (if any) from which the DNA of the invention is derived, immediately flank the gene encoding the DNA of the invention. The isolated DNA may be single-stranded or double-stranded, and may be genomic DNA, cDNA, recombinant hybrid DNA, or synthetic DNA. It may be identical to a naturally-occurring DNA sequence, or may differ from such sequence by the deletion, addition, or substitution of one or more nucleotides. The DNAs of the invention therefore include, e.g., a recombinant nucleic acid incorporated into a vector, such as an autonomously replicating plasmid or virus; a cDNA or genomic DNA fragment produced by polymerase chain reaction (PCR) or restriction endonuclease treatment; and recombinant DNA which is part of a hybrid gene encoding additional polypeptide sequences.

Also included in the isolated DNAs of the invention are single-stranded DNAs which are generally at least 10 nucleotides long, preferably at least 18 nucleotides long, more preferably at least 30 nucleotides long, and ranging up to full length of the DNAs encoding a SOK polypeptide.

The single stranded DNAs can also be complementary to a SOK coding strand, so that they can be labelled and used as hybridization probes. Preferably the isolated DNA or its complement hybridizes under stringent conditions to all or part of the nucleotide sequence shown in FIG. 1 (SEQ ID NO:1). "Stringent conditions" include, for example, hybridization at 68° C. in 5×SSC/5×Denhardt's solution/1.0% SDS, or in 0.5 M NaHPO₄ (pH 7.2)/1 mM EDTA/7% SDS, or in 50% formamide/0.25 M NaHPO₄ (pH 7.2)/0.25 M NaCl/1 mM EDTA/7% SDS; and washing in 0.2×SSC/0.1% SDS at room temperature or at 42° C., or in 0.1×SSC/0.1% SDS at 68° C., or in 40 mM NaHPO₄ (pH 7.2)/1 mM EDTA/5% SDS at 50° C., or in 40 mM NaHPO₄ (pH 7.2) 1 mM EDTA/1% SDS at 50° C. Moderately stringent conditions including washing in 3×SSC at 42° C. The parameters of salt concentration and temperature can be varied to achieve the desired level of identity between the probe and the target DNA. For guidance regarding such conditions see, e.g., Sambrook et al., Molecular Cloning, A Laboratory Manual, Cold Spring Harbor Press, Cold Spring Harbor, N.Y.; and Ausubel et al., Current Protocols in Molecular Biology, John Wiley & Sons, 1995.

DNAs of the invention can be incorporated into a vector, which may be provided as a purified preparation. DNA, either by itself, or incorporated into a vector, can be incorporated into a cell, and the cell can be propagated to form an essentially homogenous population of cells (e.g., prokaryotic cells, or eukaryotic cells such as mammalian cells)containing SOK, by methods that are well known to those skilled in the art. An "essentially homogenous" population of cells is one in which at least 99% of the cells contain the vector or the isolated DNA of the invention.

A further aspect of the invention is a method of determining whether a candidate compound modulates the expression or activity of SOK. The method includes the steps of:

a) providing a first and a second recombinant cell expressing a SOK gene;

b) introducing a candidate compound into the first recombinant cell, but not into the second cell;

c) measuring a SOK function in the first and second cells;

d) comparing the results obtained with the first and second SOK-transformed cells, wherein an increase or decrease in the SOK function in the first cell compared to the second cell is an indication that the candidate compound modulates SOK expression or activity.

In one embodiment of this method, the SOK function to be measured is activation of the gene encoding the transcription factor NFκB. In another embodiment, the function to be measured is protein kinase activity. In other embodiments, the function is arrest of the cell cycle or activation of SOK by H₂ O₂.

The invention also features a therapeutic composition that includes a SOK polypeptide or DNA as an active ingredient. Such therapeutic compositions can be formulated with a pharmaceutically acceptable carrier. In another aspect, the invention is a method of administering a therapeutically effective amount of a composition of a SOK polypeptide or DNA, or a fragment thereof, to a mammal, to treat a condition characterized by a proliferative response, e.g., to treat a vessel that has sustained balloon angioplasty-induced injury. A "therapeutically effective" amount is an amount that produces a medically desirable result in a patient.

A method of producing a SOK polypeptide is also included in the invention. In this method, cells containing an isolated DNA encoding a SOK polypeptide are cultured under conditions permitting the expression of the SOK polypeptide, and the SOK polypeptide is isolated. Also included in the invention are therapeutic compositions that include DNAs encoding a SOK polypeptide.

In another aspect, the invention is a substantially pure antibody which specifically binds SOK. An antibody that "specifically binds" to SOK binds to SOK and does not substantially recognize and bind to other antigenically-unrelated molecules. Antibodies according to the invention can be prepared by a variety of methods. For example, a SOK protein or antigenic fragment thereof can be administered to an animal in order to induce the production of polyclonal antibodies. Alternatively, the antibodies can be monoclonal antibodies. Such monoclonal antibodies can be prepared using hybridoma technology (see, e.g., Kohler et al., Nature 256:495 (1975); Kohler et al., Eur. J. Immunol. 6:292 (1976); Kohler et al., Eur. J. Immunol. 6:511 (1976); Hammerling et al., In Monoclonal Antibodies and T Cell Hybridomas, Elsevier, N.Y., 1981).

As used herein, "substantially pure" describes a molecule, e.g., a protein, that is substantially free from the components that naturally accompany it. Typically, a compound is substantially pure when at least 60%, more preferably at least 75%, more preferably at least 90%, and most preferably at least 99%, of the total material in a sample is the molecule of interest.

Individuals skilled in the art will recognize that the compositions of the invention can be assembled in a kit for the detection of SOK polypeptides or RNA. Typically, such kits include reagents containing the DNAs or antibodies of the invention with instructions and suitable packaging for their use as part of an assay for SOK. For example, a kit can contain an anti-SOK antibody that is capable of specifically forming an immunocomplex with SOK in a sample, a solid support to which the antibody is bound, and means to detect the immunocomplex.

In another aspect, the invention features a kinase inactive mutant of a SOK polypeptide, or a DNA encoding such a mutant. By "kinase inactive mutant" is meant a SOK polypeptide which has been altered so that the kinase domain is less active than in the wild-type SOK. Such mutants preferably show 50% or less of the kinase activity of wild-type SOK; more preferably, 25% or less; more preferably, 10% or less; and most preferably, 5% or less of the kinase activity of wild-type SOK. One embodiment is a kinase inactive mutant of SOK-1, in which the invariant lysine in the ATP binding site has been substituted with an arginine.

The invention also features a therapeutic composition containing a kinase inactive mutant of a SOK polypeptide, or DNA encoding such a mutant, as an active ingredient. In another aspect, the invention features a method of downregulating the gene encoding NFκB by administering a therapeutically effective amount of a kinase inactive mutant of a SOK polypeptide, or a DNA encoding such a kinase inactive mutant.

Biologically active fragments of SOK polypeptides, and DNAs encoding such polypeptides, are also included in the invention. An example of such an active fragment is the portion of the SOK-1 polypeptide corresponding to the noncatalytic carboxy terminal region of SOK-1. A "biologically active" fragment is a fragment having at least 10% of the activity of SOK in specific functions, e.g., induction of cell cycle arrest. For example, a biologically active fragment can have 30%, 50%, 80%, 90% or up to 100% or more of the activity of SOK. Such fragments include that encoded by amino acids 286 to 426 of SOK-1 (SEQ ID NO:2), and that encoded by amino acids 286 to 336 of SOK-1(SEQ ID NO:2). Therapeutic compositions of the invention include such active fragments, or DNAs encoding such fragments, formulated with a pharmaceutically acceptable carrier. A therapeutically effective amount of such a composition is administered to a patient, e.g., to treat a condition characterized by a proliferative response, such as balloon angioplasty-induced injury, inflammatory responses, or cancer.

Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which the invention pertains. All publications mentioned herein are incorporated by reference. The examples which follow are illustrative only, and not intended to be limiting.

Other advantages and features of the invention will be apparent from the detailed description, and from the claims.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a diagram of the nucleotide (SEQ ID NO:1) and predicted amino acid (SEQ ID NO:2) sequences of human SOK-1.

FIG. 2 is a diagram showing an alignment of the amino acid sequence of the catalytic domain of SOK-1 with the amino acid sequence of the catalytic domains of Ste20 (SEQ ID NO:4) other Ste20 homologs (PAK1 (SEQ ID NO:3), MST1 (SEQ ID NO:5) Sps1 (SEQ ID NO:6), and GCK (SEQ ID NO:7)).

FIG. 3 is an autoradiogram of a Northern blot of RNA from various tissues, hybridized to a SOK-1 probe.

FIG. 4A is an autoradiogram of a Western blot of cells transfected with a HA epitope tagged-SOK-1 gene, probed with anti-HA antibody.

FIG. 4B is an autoradiogram of cells transfected with a HA epitope-tagged SOK-1 and immunoprecipitated with anti-HA antibody, followed by immune complex kinase assay using MBP as substrate.

FIGS. 5A-F are immunofluorescent stains of SOK-1-transfected cells, showing the subcellular localization of SOK-1.

FIG. 6 is a diagram showing the effect of Protein Phosphatase 2A (PP2A) and autophosphorylation on SOK activity.

FIG. 7 is a diagram showing the effect of the C-terminal non-catalytic region on SOK-1 kinase activity.

FIG. 8 is a diagram showing the kinetics of activation of SOK-1 by H₂ O₂.

FIG. 9A is a diagram showing the effect of SOK-1 on the p38 cascade.

FIG. 9B is a diagram showing the effect of SOK-1 on the ERK1 cascade.

DETAILED DESCRIPTION

Mammalian homologs of the yeast serine/threonine protein kinase, Ste20, can be divided into two groups based on their regulation and structure. The first group, the Ste20 family, includes PAK1 and is regulated by Rac1 and cdc42Hs. Activators of protein kinases in the Ste20 family have been identified. In contrast, little has been known about activators, regulatory mechanisms or physiological roles of the second family, the Sps1 family, which includes GC kinase and MST1. The present invention is based on the identification, cloning and characterization of a human Ste20 homolog, SOK-1. Like members of the Sps1 family of Ste20 homologs, SOK-1 is characterized by an amino terminal catalytic domain. SOK-1 is positively regulated by phosphorylation, and is negatively regulated by its noncatalytic carboxy terminal region. There is no significant sequence similarity between this noncatalytic regulatory region and any other protein kinases.

SOK-1 is markedly activated by depletion of intracellular ATP stores, an important component of ischemia. This novel protein kinase is also activated by oxidant stress, and is the first mammalian Ste20 known to be activated by any cellular stress. This novel protein kinase is not activated by growth factors, alkylating agents, cytokines or environmental stresses including heat shock and osmolar stress. SOK-1 does not act as part of a generalized stress response pathway, but is activated relatively specifically by oxidant stress. Oxidant stress is a prominent component of ischemia and of reperfusion of ischemic tissue.

SOK-1 activates the transcription factor NFκB, which is implicated in a host of pathological conditions including inflammation and autoimmune syndromes. A kinase inactive mutant of SOK-1 can inhibit NFκB activity. SOK-1 also induces cell cycle arrest via a pathway that is independent of other stress activated protein kinases known to effect cell cycle arrest. This cell cycle arrest is mediated by the noncatalytic subunit of SOK-1.

Unlike GC kinase, a member of the Ste20 family, and PAK1, a member of the Sps1 family, SOK-1 does not activate any of the known MAPK pathways, such as SAPK/JNK, p38 or ERK1/-2. SOK-1 thus defines a novel stress response pathway which is likely to include a unique stress-activated MAP kinase cascade. The data suggest that SOK-1 functions similarly to yeast Ste20s, which transduce signals in response to environmental stress.

Materials and Methods

Isolation and analysis of SOK-1 cDNA

Degenerate sense [GA(A/G) (C/T)TIATGGCIGTIAA(A/G)CA] (SEQ ID NO:8) and antisense [TTIGCICC(T/C)TTIAT(A/G)TCIC(G/T) (A/G)TG] (SEQ ID NO:9) primers were used to amplify DNA from a human placenta cDNA library using Taq polymerase. The PCR products were ligated into the pCRII vector (Invitrogen). A 305 bp fragment was obtained which was not in the database but which had significant homology to the catalytic domain of protein serine/threonine kinases. This fragment was used to screen 500,000 plaques from a human B cell cDNA library in λYES (provided by Stephen J. Elledge, Department of Biochemistry, Baylor College of Medicine). Seven positive clones were isolated, and those containing the largest inserts were analyzed by DNA sequencing of both strands using the dideoxy chain termination method with Sequenase 2.0 (USB, Inc.). DNA and amino acid sequence comparisons were made using the University of Wisconsin Genetics Computer Group programs BLAST, Pileup, and Bestfit, and the BEAUTY (BLAST Enhanced Alignment Utility) and BLASTPAT (BLAST PATtern database search tool) programs from the Human Genome Center, Baylor College of Medicine.

Northern blot analysis

Total RNA was isolated from rat organs by the guanidinium thiocyanate-phenol-chloroform method (Witzgall et al., Mol. Cell. Biol. 13:1933 (1993)). Twenty μg of total RNA was size-fractionated on a 1% formaldehyde-agarose gel and transferred to GeneScreen Plus (NEN) membrane as described. Id. Blots were hybridized with a 409-bp HindIII-BamHI fragment from the 3' half of SOK-1 (nucleotides 995-1403) which included 284 bp of open reading frame encoding part of the non-catalytic region, and 125 bp from the 3' untranslated region. This probe was labelled with [α]-³² P dCTP by random priming. Hybridization was carried out for 18 hours at 45° C. in 5×SSPE (1×SSPE: 150 mM NaCl, 10 mM NaH₂ PO₄, 0.7 mM EDTA), 44% formamide, 5×Denhardt's solution, 1% SDS, 10% Dextran Sulfate, and 100 μg/ml denatured salmon sperm DNA. The membranes were washed twice for 15 minutes at room temperature in 2×SSPE, twice for 30 minutes at 65° C. in 2×SSPE with 2% SDS, and once for 30 minutes at room temperature in 0.2×SSPE. Membranes were exposed to X-ray film for 5 days at -70° C. with intensifying screens.

Plasmids

Plasmids used included pMT3 (pMT2 modified to include sequence encoding the 9 amino acid hemagglutinin (HA) epitope N-terminal to the insert) (Pombo et al., Nature 377:750 (1995)), pCMV5 (a CMV-based vector including sequence encoding the 9 amino acid M2 epitope tag N-terminal to the insert), pEBG (a vector that is driven by the human EF-1α promoter and that includes sequence encoding glutathione s-transferase (GST) N-terminal to the insert) (Pombo et al., Nature 377:750 (1995); Sanchez et al., Nature 372:794 (1994)), and pGEX-KG (a prokaryotic expression vector that includes sequence encoding GST N-terminal to the insert) (Guan et al., Anal. Biochem. 192:262 (1991)).

To create pCMV5-SOK-1ΔC, pCMV5-SOK-1 was cut with HindIII and then religated. The pCMV5-SOK-1ΔC construct contains sequence encoding amino acids 1-333 and includes the entire kinase domain of SOK-1, but not the carboxy terminal 93 amino acids of the protein. pEBG-SAPKpS4β, pEBG-p38, pEBG-ERK1 contain the three MAP kinases p54β (the β isoform of the SAPK, p54), p38, and ERK1, respectively, as GST fusion proteins. pRSV-BXB-Raf-1 encodes a variant of c-Raf-1 lacking the regulatory domain. BXB-Raf-1 is constitutively active and transforming (Bruder et al., Genes & Development 6:545 (1992); Pombo et al., Nature 377:750 (1995); Sanchez et al., Nature 372:794 (1994)).

Transfection protocols and kinase assays

Subconfluent COS7 cells were transfected using the DEAE-dextran technique as described (Pombo et al., Nature 377:750 (1995)). One to ten μg of expression plasmid DNA were used per plate and adjusted to a total of 20 μg of DNA with the appropriate empty vector. Forty-eight hours after transfection, cells were exposed to various stimuli or vehicle, and extracts were prepared as described (Pombo et al., Nature 377:750 (1995); Pombo et al., J. Biol. Chem. 269:26546 (1994)). Extracts were exposed to anti-HA or anti-M2 (Kodak) monoclonal antibodies, or to an anti-SOK-1 rabbit polyclonal antibody (see below) for 3 hours, and immune complexes were collected with Protein G-Sepharose beads. Beads were washed three times in lysis buffer, three times in LiCl buffer (500 mM LiCl, 100 mM Tris-HCl, pH 7.6), and three times in assay buffer (Pombo et al., J. Biol. Chem. 269:26546 (1994)). Kinase assays were started by the addition of myelin basic protein (MBP, for SOK-1 and ERK1); GST-c-Jun (amino acids 1 to 135), containing the transactivation domain of c-Jun (for SAPK) (Kyriakis et al., Nature 369:156 (1994); Pombo et al., Nature 377:750 (1995); Pombo et al., J. Biol. Chem. 269:26546 (1994)); or ATF-2 (amino acids 8 to 94), containing the transactivation domain of ATF-2 (for p38) (Morooka et al., J. Biol. Chem. 270:30084 (1995)), in the presence of [γ]-³² P-ATP (100 μM, 3000-9000 cpm/pmole) and MgCl₂ (10 mM) After 5 to 20 minutes at 30° C., the kinase reactions were stopped with Laemmli sample buffer. Following SDS-polyacrylamide gel electrophoresis and autoradiography, the bands corresponding to the substrate were cut out of the gel and radioactivity was determined by liquid scintillation counting. For all kinase assays, an aliquot of the cell lysate was run on an SDS-polyacrylamide gel, transferred to Imobilon, and subjected to immunoblotting with the appropriate antibody to ensure equivalent expression of the kinases (Morooka et al., J. Biol. Chem. 270:30084 (1995)). Antibody binding was detected using the Enhanced Chemiluminescence System.

Phosphatase Inactivation and Reactivation Experiments

Six 10 cm dishes of COS7 cells were transfected with pMT3-SOK-1. Forty eight hours later, cell lysates were subjected to immunoprecipitation with anti-HA antibody. Immune complexes were divided into equal aliquots and then incubated for 20 minutes at 30° C. with the catalytic subunit of protein phosphatase 2A (PP2A), either with or without the PP2A inhibitor, okadaic acid (100 nM). PP2A was purified from rabbit skeletal muscle (Chen et al., Science 257:1261 (1992)) and was generously provided by Dr. David Brautigan (Center for Cell Signalling, University of Virginia Health Science Center). After the 20 minute incubation, okadaic acid was added to bring the final concentration to 100 nM in all tubes. Immune complexes were washed twice with kinase assay buffer, and then exposed to [γ]-³² P-ATP (100 μM) for 0, 5, 10, or 20 minutes prior to the addition of MBP and subsequent kinase assay for 5 minutes at 30° C.,

Production of anti-SOK-1 polyclonal antibodies

A peptide (amino acids 333-426) from the non-catalytic region of SOK-1 was used to generate a polyclonal rabbit antibody. This peptide was expressed in bacteria from PGEX-KG as a GST fusion protein, purified, and used to immunize rabbits according to standard protocols (Harlow et al., Antibodies: A Laboratory Manual, Cold Spring Harbor Laboratory, Cold Spring Harbor, N.Y. (1988)). The antibodies from each of two rabbits recognized 1 ng of GST-SOK1 on a Western blot when used at a 1:1000 dilution. In addition, at a 1:250 dilution, the antibody immunoprecipitated HA-SOK-1 from lysates of transfected cells.

Production of anti-SOK-1 monoclonal antibodies

Monoclonal antibodies can be generated using the standard Kohler and Milstein technique.

Microinjection and immunofluorescence

Mouse fibroblast NIH 3T3 cells were grown on glass coverslips and microinjected with the pMT3-SOK-1 expression vector, encoding SOK-1 with the HA epitope tag at its amino terminus. Plasmid DNA was purified twice on a CsCl gradient and extracted three times with phenol and chloroform. Cells were injected in a 3.5 cm dish with an automated microinjection system (AIS; Zeiss (Ansorge et al., J. Biochem Biophys. Meth. 16:283 (1988)) at a pressure between 80 and 170 kPa. The computer settings were as follows: angle, 45°; speed, 10; and time, 0.0 sec. Plasmid DNA was injected at a concentration of 100 μg/ml concentration (Pagano, Genes & Development 8:1627 (1994)). Twenty-four hours after injection, the cells were fixed with 4% paraformaldehyde for 15 minutes, treated with 0.1% SDS in phosphate buffered saline (PBS) for 5 minutes, and permeabilized with 0.5% Triton X100 (in PBS) for 15 minutes. Cells were then processed for immunofluorescence (Brown et al., Histochem. Cell. Biol., 105:261 (1996).

All antibodies were diluted in Dulbecco's modified Eagle's medium containing 10% calf serum. Coverslips were incubated with affinity purified anti-HA antibody (Boehringer Mannheim) at a final concentration of 0.026 mg/ml for one hour. After incubation for 40 minutes in biotinylated goat anti-mouse antibody (Jackson Laboratories) which was diluted 1:50, the coverslips were incubated for 40 minutes in fluorescein isothiocyanate conjugated streptavidin, diluted 1:100 (Jackson Laboratories). All incubations were carried out at 37° C. in a humidified chamber. Between each step, cells were washed three times with PBS. Nuclei were counterstained with bisbenzimide (Hoescht 33258) for 2 minutes at 1 mg/ml in PBS. Coverslips were mounted in Crystal/Mount (Biomedia) and visualized on a Zeiss Axiovert 100 photomicroscope. Cells were imaged with a Bio-Rad Laser Scanning Confocal Microscope.

Derivation of SOK-1 kinase inactive mutants

A kinase inactive mutant of SOK-1 was derived by mutating the ATP binding site of SOK-1, by replacing the invariant lysine with arginine.

Identification and Characterization of SOK-1, a Novel Ste20 Homolog

Screening of the human B cell cDNA library identified two clones of 1.8 kb and 2.0 kb. The nucleotide sequence of the gene encoded by these overlapping clones, and the deduced amino acid sequence of the protein encoded by this gene, are shown in FIG. 1. For the nucleotide sequence, numbers refer to the position of the codon relative to the initiator ATG. The predicted translation product is indicated below the nucleotide sequence, and the numbers refer to the position of the amino acid relative to the initial methionine. The 2.0 kb clone contains a Kozak sequence (gcggccatgg), SEQ ID NO:10 at a candidate initiation codon (FIG. 1). There is an in-frame stop codon 15 bp 5' of this initiation codon. There are no other candidate initiation codons between this stop codon and the ATG, which suggests that this codon is the true translation start site. A poly (A) tail is present at the 3' end of the 1.8 kb clones.

The open reading frame encodes a protein which is 426 amino acids in length and has a predicted molecular mass of 48,041 daltons. The kinase domain is located in the amino terminal half of the protein and contains all 11 subdomains of serine/threonine kinases (Hanks et al., In Methods in Enzymology, Hunter et al., eds., Academic Press, San Diego, Calif., pp. 200:38-62 (1991)). Alignment of the catalytic domain of SOK-1 with the catalytic domains of the five most closely related kinases as determined by the BLAST and Bestfit programs is shown in FIG. 2. The deduced amino acid sequences of PAK1 (SEQ ID NO:3) (Manser et al., Nature 367:40 (1994)); Ste20 (SEQ ID NO:4) (Leberer et al., EMBO J. 11:4815 (1993)); MST1 (SEQ ID NO:5) (Creasy et al., J. Biol. Chem. 270:21695 (1995)); Sps1 (SEQ ID NO:6) (Friesen et al., Genes & Development 8:2162 (1994)); and GC kinase (SEQ ID NO:7) (Katz et al., J. Biol. Chem. 269:16802 (1994)) were aligned by eye after being aligned with the Pileup program. Gaps, which were introduced to maintain alignment, are denoted by dots. Roman numerals indicate the eleven protein serine/threonine kinase subdomains (Hanks et al., In Methods of Enzymology, Hunter et al., eds., pp. 200:38-62, Academic Press, Inc., San Diego, Calif. (1991)). Residues that are conserved in all family members are enclosed in boxes. Comparison of the amino acid sequence of the catalytic domain with other protein kinases using the BLAST program identified the yeast kinase, Sps1 (Friesen et al., Genes & Development 8:2162 (1994)), and the mammalian kinases, MST1 (Creasy et al., J. Biol. Chem. 270:21695 (1995)) and GC kinase (Katz et al., J. Biol. Chem. 269:16802 (1994)) as its closest homologs. Within the catalytic domain, SOK-1 was 50% identical and 68% similar to Sps1, 56% identical and 73% similar to MST1, and 51% identical and 68% similar to GC kinase.

The five kinases most closely related to SOK-1 are Sps1, MST1, GC kinase, Ste20 (Leberer et al., EMBO J. 11:4815 (1993)), and PAK1 (Manser et al., Nature 367:40 (1994)), all of which are Ste20 homologs. Alignment of the amino acid sequence of the catalytic domains of Sps1 and Ste20 with SOK-1 indicates a high degree of evolutionary conservation (FIG. 2). Comparison of the amino acid sequence of the C-terminal non-catalytic region of SOK-1 with the database using the BLAST, BEAUTY, and BLASTPAT programs failed to identify regions of significant homology with any other kinases.

SOK-1 is thus related to the Sps1 family of Ste20s on the basis of its organization, i.e., amino terminal catalytic domain, and sequence similarity within the kinase domain to the Sps1 group. SOK-1 is more similar in sequence to Sps1 (50% identical) than it is to Ste20 (42% identical). Furthermore, Sps1 is more similar to SOK-1 than Sps1 is to Ste20 (44% identical)

SOK-1 Expression

mRNA was extracted from various rat tissues and subjected to Northern blot analysis using a probe from the carboxy terminal non-catalytic region of SOK-1. Expression of a 2300 bp mRNA was detected in all tissues examined except stomach, where the probe hybridized to two transcripts, one of approximately 2600 bp and one of 1500 bp (FIG. 3). Highest levels of expression were in testis, large intestine, brain, and stomach. Intermediate levels of expression were seen in heart and lung. Equal loading of all lanes in the gel was confirmed by ethidium bromide staining. The kinase was expressed in the two human B cell lines examined, Ramos, a Burkitt lymphoma cell line that has features of a germinal center B cell, and HS Sultan, a mature B cell line.

COS7 cells were transfected with pMT3-SOK-1, which encodes a SOK-1 protein with a nine amino acid HA epitope tag on the amino terminus. The results of Western blotting using a monoclonal anti-HA antibody as a probe of the pMT-3-SOK-1 transfected cells (+), as well as cells transfected with the vector without the SOK-1 insert (-) are shown in FIG. 4A. Transfection with pMT3-SOK-1, but not the vector alone, resulted in expression of a protein with an approximate molecular weight of 50 kDa (indicated by the arrow in FIG. 4A). The kinase displayed a high degree of constitutive activity toward MBP in immune complex kinase assays. The results of a typical experiment in which COS7 cells were transfected with pMT3 vector alone (-), or 1 μg (1) or 5 μg (5) pMT3-SOK-1 is shown in FIG. 4B. Forty eight hours after transfection, the cells were harvested and lysates were subjected to immunoprecipitation with anti-HA antibody followed by immune complex assay using MBP as substrate. Phosphoamino acid analysis demonstrated that the kinase phosphorylated MBP on serine and threonine residues, but not on tyrosine.

To determine subcellular localization of SOK-1, pMT3-SOK-1, encoding HA-SOK-1, was microinjected into NIH3T3 fibroblasts at a concentration of 100 μg/ml. HA-SOK-1 was detected by staining with the anti-HA antibody as described supra. SOK-1 was localized almost exclusively in the cytoplasm (FIGS. 5B and 5E). A representative slice of 0.2 μm of the same cells is also shown in FIGS. 5A and 5D. The cells were counterstained with Hoescht 33258 to visualize the nuclei (FIGS. 5C and 5F).

Regulation of SOK-1

The role of phosphorylation in the regulation of SOK-1 was explored. Exposure of SOK-1 to protein serine phosphatase 2A (PP2A) in immune complexes reduced SOK-1 kinase activity by approximately 40%. This effect of PP2A was prevented by co-incubation with the PP2A inhibitor okadaic acid (OA). To determine whether autophosphorylation might play a role in activating SOK-1, the protein was partially inactivated by PP2A, then incubated with γ-³² P-ATP (100 μM) and assayed for reactivation (FIG. 6). Reactivation of SOK-1 kinase activity which correlated with phosphorylation of a 50 kDa protein in the immune complex. The increase in kinase activity over time correlated with the degree of phosphorylation. The phosphorylated protein also demonstrated enhanced electrophoretic mobility after PP2A treatment and retarded mobility after incubation with ATP (FIG. 6). The data thus suggest that phosphorylation, probably autophosphorylation, is an important mechanism of activation of SOK-1.

Autophosphorylation and autoactivation of a kinase in immune complexes, if unrecognized, greatly complicates the identification of activators. After a twenty minute incubation in the presence of ATP, MBP kinase activity of SOK-1 previously inactivated by PP2A, was equal to that of SOK-1 which had not been inactivated by PP2A (FIG. 6). Autophosphorylation and autoactivation may explain the difficulty which has been encountered in identifying activators of the Sps1 family of Ste20 homologs when standard immune complex kinase assays are performed. Under these conditions, no activators of MST1 were identified (Creasy et al., J. Biol. Chem. 270:21695 (1995)), and for GC kinase, TNFα only weakly stimulated kinase activity. Since SOK-1 is markedly activated by autophosphorylation in immune complex kinase assays, incubations for kinase assays of longer than 5 minutes can be expected to mask any differences between control and stimulated cells. Consequently, all subsequent kinase assays were performed for 5 minutes.

SOK-1 has an amino terminal catalytic domain, placing it, on the basis of organization, in the Sps1 group of Ste20s, which includes Sps1, GC kinase, and MST1. These kinases lack the Rac1/cdc42Hs binding domain present in the regulatory domains of Ste20 and the PAK family of kinases, and the role of their carboxy terminal non-catalytic regions is unclear. The ability of the carboxy terminal region of SOK-1 to regulate kinase activity in transfected COS7 cells was tested (FIG. 7). Using MBP as a substrate, the kinase activity of SOK-1, expressed from pCMV5-SOK-1, which encodes SOK-1 with a nine amino acid M2 epitope tag at the amino terminus, was compared with that of M2-SOK-1ΔC, a deletion mutant containing the catalytic domain but missing the carboxy terminal 95 amino acids of the non-catalytic region, and pCMV5, which is the vector containing the M2 epitope tag, but lacking the SOK-1 sequences. Although the cellular extracts were matched for total protein prior to immunoprecipitation with anti-M2 antibody, immunoblots of the extracts revealed that M2-SOK-1ΔC was expressed at a much lower level than full-length M2-SOK-1 (FIG. 7, bottom). Despite the lower expression of M2-SOK-1ΔC, and the presence of much less M2-SOK-1ΔC compared to full-length M2-SOK-1 in the immunoprecipitates, kinase activity, measured as phosphorylation of MBP, was equivalent, consistent with significantly greater specific activity of M2-SOK-1ΔC (FIG. 7). These data suggest that the carboxy terminal non-catalytic region inhibits kinase activity of SOK-1 and is the first demonstration of a role for the non-catalytic region of protein kinases related to the Sps1 group of Ste20s. Inhibition of activity may be due to binding of the carboxy terminal region to the catalytic domain, since the carboxy terminal region (lacking the kinase domain) co-immunoprecipitates with SOK-1ΔC when the two are co-expressed. The carboxy terminal region may exert its inhibitory effect by preventing access by an activator, possibly SOK-1 itself, to a critical site within the catalytic domain, or by inhibiting interaction of the kinase domain with substrates.

SOK-1 is thus regulated by its non-catalytic region, and by phosphorylation. Identification of these two regulatory mechanisms suggests that the regulation of SOK-1 may be similar to the regulation of PAK1. Binding of the inhibitory regulatory region of PAK1 to the small GTP binding proteins appears to allow the kinase to undergo autophosphorylation, which activates the kinase. For SOK-1, binding of the inhibitory regulatory region to an as yet unidentified activator may also allow autophosphorylation and activation to occur. Thus, the primary mechanism of activation of PAK1 and SOK-1 (and possibly other Ste20s) would be similar (autophosphorylation), but the activators to which the regulatory domains bind, allowing autophosphorylation to occur, would differ. Specificity in the activation of Ste20s (and subsequently, MAP kinase cascades) in response to a stimulus could be determined by protein or lipid interaction domains within the regulatory region.

Activation of SOK-1 by depletion of ATP stores

SOK-1 is markedly activated by the depletion of intracellular ATP stores, an important component of ischemia. Ischemia is a major cause of morbidity and mortality, and clinically presents as myocardial infarction, stroke, and acute renal failure. Several kinases are activated after reperfusion or after repletion of ATP stores, but SOK-1 is activated during the phase of ATP depletion, suggesting that it is a very early modulator of the response to ATP depletion and therefore ischemia.

Activation of SOK-1 by H₂ O₂

Incubation of Ramos B cells with okadaic acid (1 μM, 20 minutes) activated SOK-1 (Table 1), compatible with regulation of SOK-1 (and/or an upstream activator) by phosphorylation. Numerous agonists that were representative of multiple different classes of stimuli were also tested for their ability to activate SOK-1. Only H₂ O₂ consistently activated SOK-1 when native kinase was assayed after immunoprecipitation from Ramos B cells or when HA-tagged SOK-1 was assayed after immunoprecipitation from transfected COS7 cells (Table 1). H₂ O₂ (0.5 mM) activated SOK-1 approximately 3-fold (p<0.01). No H₂ O₂ -induced increase in MBP kinase activity was detected when immunoprecipitation was performed with preimmune serum. Activation of SOK-1 was evident as early as 10 minutes following exposure of Ramos B cells to H₂ O₂, peaked at 20 minutes, and remained elevated at 60 minutes (FIG. 8). Activation was evident at 0.1 mM, the lowest concentration tested (2.1-fold increase in kinase activity). SOK-1 is thus markedly activated by oxidant stress. Oxidant stress is a prominent component of ischemia, and of reperfusion of ischemic tissue. Oxidant stress also occurs with ionizing radiation, such as ultraviolet or gamma radiation, and is an important element of inflammation.

This is the first clear demonstration of activation of a member of this group of Ste20s by any stimulus. The activation of SOK-1 by H₂ O₂ not only identifies a new oxidant stress response signal transduction pathway, but also suggests that one role of this and possibly other Ste20s of this group is to respond to environmental stresses just as their homologs do in the simplest eukaryotes. The survival of aerobic organisms depends upon their mounting an effective response to oxidant stress. Activation by oxidant stress suggests that SOK-1, and possibly other as yet unidentified SOK-1 homologs, may, like the Ste20s identified thus far in yeast, play an important role in the responses of the cell to environmental stress.

In contrast to activation of SOK-1 by H₂ O₂, potent activators of the ERK1/-2 cascade, such as epidermal growth factor (EGF), platelet-derived growth factor (PDGF) and the phorbol ester phorbol myristate acetate (PMA) combined with the calcium ionophore, ionomycin, did not activate SOK-1 (Table 1). In the same COS7 cells, these agonists activated ERK1, expressed in pEBG, 5- to 7-fold. Oxidant stress appeared to be a specific activator among the several cellular stresses tested. Specifically, high and low osmolar stress, heat shock, tumor necrosis factor α (TNFα), and anisomycin, which potently activate the SAPK and/or p38 cascades in these and other cells (see Figs. and Galcheva-Gargova et al., Science 265:806 (1994); Han et al., Science 265:808 (1994); Kyriakis et al., Nature 369:156 (1994); Pombo et al., Nature 377:750 (1995); Rouse et al., Cell 78:1027 (1994)), did not activate SOK-1. Platelet activating factor, which signals via a heterotrimeric G protein-coupled receptor and is a potent activator of intracellular Ca²⁺ transients in Ramos cells, was also ineffective.

                  TABLE 1                                                          ______________________________________                                         Fold-activation of native SOK-1 in Ramos B                                       cells and HA-SOK-1 in COS7 cells.                                                Agonist               Ramos   COS7                                         ______________________________________                                         H.sub.2 O.sub.2 (0.5 mM, 20 min)                                                                     2.9     2.8                                                Okadaic acid (1 μM, 30 min) 2.3 --                                          Interferon-γ (50 ng/ml, 20 min) 1.0 --                                   TNFα (50 ng/ml, 20 min) 1.5 0.9                                          Anti-Ig (20 min) 0.8 --                                                        Platelet activating factor (1 μM, 20 min) 1.4 --                            PMA/Ionomycin (300 nM/1 μM, 20 min) 1.4 1.4                                 Nitrogen mustard (10 μM, 30 min) 1.2 1.4                                    Cyclophosphamide (10 μM, 30 min) 0.9 1.5                                    cisplatin (10 μM, 30 min) 1.0 1.1                                           Heat shock (42° C., 5 min) -- 0.9                                       Anisomycin (50 μg/ml, 20 min) -- 1.1                                        Hyperosmolarity (NaCl 700 mM, 15 min) -- 0.9                                   Hypoosmolarity (150 mOsm, 15 min) -- 0.9                                       EGF (100 ng/ml, 10 min) -- 1.3                                                 PDGF (20 ng/ml, 10 min) 1.0 1.2                                              ______________________________________                                          -- = not determined.                                                     

Native SOK-1 in Ramos B cells was assayed with MBP as substrate after immunoprecipitation with rabbit polyclonal anti-SOK-1. HA-SOK-1 was assayed after immunoprecipitation with anti-HA antibody from extracts of COS7 cells which had been transfected with pMT3-SOK-1 (5 μg per 10 cm dish).

Hypoosmolar stress was induced by placing cells in Krebs-Henseleit buffer without NaCl (Pombo et al., J. Biol. Chem. 269:26546(1994).

Reactive oxygen radicals, via damage to many cellular components including DNA, can cause cell death, or if less severe, cell cycle arrest at either the G₁ or G₂ checkpoint (Russo et al., J. Biol. Chem. 270:29386 (1995)). DNA damage not only activates checkpoint controls, but may also activate protein kinases, including the SAPKs, c-Raf-1, and ERKs, which are integral components of cytoplasmic signal transduction cascades, as well as the non-receptor tyrosine kinase c-abl (Hibi et al., Genes & Development 7:2135 (1993); Kharbanda et al., Nature 376:785 (1995); Kharbanda et al., J. Biol. Chem. 270:18871 (1995); Livingstone et al., EMBO J. 14:1785 (1995); Radler-Pohl et al., EMBO J. 12:1005 (1993); Russo et al., J. Biol. Chem. 270:29386 (1995); Van Dam et al., EMBO J. 14:1798 (1995)). In order to determine whether activation of SOK-1 was likely to be triggered by DNA damage or by oxidant stress acting via a DNA damage-independent mechanism, alkylating agents were tested for their ability to activate SOK-1. Alkylating agents activate the DNA damage-induced checkpoint controls and protein kinases, but do not produce oxidant stress. Exposure of transfected COS7 cells to the alkylating agents cyclophosphamide, nitrogen mustard, and cisplatin did not activate SOK-1, suggesting that oxidant stress-induced activation of SOK-1 is not mediated by DNA damage response pathways. Thus, activation of SOK-1 by oxidant stress is not part of a generalized response to either cellular or genotoxic stress. Cross-linking surface IgM on Ramos B cells with anti-Ig antibody coupled to beads, which induces apoptosis in these cells, did not activate SOK-1 but did markedly enhance tyrosine phosphorylation of several proteins in these cells.

Although these data clearly place SOK-1 on an oxidant stress response pathway, SOK-1 does not appear to activate the known stress-activated MAP kinase pathways. It has recently been reported that SOK-1 (previously called UK-1; the name was changed to SOK-1 to reflect the fact that the kinase is activated by oxidant stress), unlike the closely related GC kinase, did not activate the SAPKs in co-transfection experiments (Pombo et al., Nature 377:750 (1995)). Co-transfection of HA-SOK-1 with the other MAP kinases, p38 (FIG. 9A) and ERK1 (FIG. 9B), both expressed in pEBG, did not result in the activation of the MAP kinases. In the p38 experiments, COS7 cells were transfected with pEBG vector (p38-) or pEBG encoding p38 as a GST fusion protein (p38+), and either pMT3 vector (SOK-1-) or pMT3 encoding HA tagged SOK-1 (SOK-1+). To confirm that p38 could be activated, cells were exposed to NaCl (500 mM) for 10 minutes (0NaCl+). p38 kinase activity was assayed with ATF-2 (8-94) as substrate (Morooka et al., J. Biol. Chem. 270:30084 (1995)). p38 was markedly activated by exposure of cells to osmolar stress.

In the ERK1 experiments, COS7 cells were transfected with pEBG vector (ERK1-) or pEBG encoding ERK1 as a GST fusion protein (ERK1+), and either pMT3 vector (SOK-1-), pMT3 encoding HA-tagged SOK-1 (SOK-1+), or as a positive control, pMT3 encoding BXB-Raf (+), a constitutively active c-Raf-1 that is missing the amino terminal regulatory domain (Bruder et al., Genes & Development 6:545 (1992)). ERK1 assays were performed in duplicate with MBP as substrate. As shown in FIG. 9B, ERK1 was activated by co-transfection of pRSV-BXB-Raf-1, but not SOK-1.

Oxidant stress activates the ERKs, and may activate the SAPKs somewhat (Kyriakis et al., Nature 369:156 (1994); Russo et al., J. Biol. Chem. 270:29386 (1995)), but SOK-1 does not appear to be implicated in this activation. SOK-1 did not activate any of four MAP kinase cascades, including SAPKs (Pombo et al., Nature 377:750 (1995)); p38 (FIG. 9A); ERK1 (FIG. 9B); or MEK5/ERK5 (Zhou et al., J. Biol. Chem. 270:12665 (1995)), further indicating that the stress response pathway regulated by SOK-1 is unique. Since evolutionary conservation of the activation of MEKK/MEK/MAPK cascades by Ste20s extends to mammals (Polverino et al., J. Biol. Chem. 270:26067 (1995)); Pombo et al., Nature 377:750 (1995); Zhou et al., J. Biol. Chem. 270:12665 (1995)), and all Ste20s identified to date in yeast or mammals, with the exception of MST1 (Creasy et al., J. Biol. Chem. 270:21695 (1995)) have been shown to activate one or more MAP kinase cascades, it is likely that SOK-1 controls a novel oxidant stress-activated MAP kinase cascade.

SOK-1 Functions

NFκB is a ubiquitously expressed transcription factor that is believed to be critical to diverse processes including T lymphocyte activation, the expression of cellular adhesion molecules, and the expression of interferon β. NFκB appears to play vital roles in transplant rejection, post-ischemic injury, the response to viral infection, and inflammation. Many diverse genes are believed to be under the control of NFκB. NFκB is activated by cytokines, such as TNFα, IL-1β, and IL-2; lipopolysaccharide, the mediator of septic shock; viruses, including Human T Cell Leukemia Virus Type 1, Human Immunodeficiency Virus 1, and Hepatitis B; ultraviolet and X-irradiation; antigen stimulation of T and B lymphocyte receptors; and the tumor promoting phorbol esters. In addition, most, if not all, of the activators of NFκB result in oxidant stress. Therefore, SOK-1 could be a final common pathway for activation of NFκB, and SOK-1 having an inactive kinase domain could be a general inhibitor of NFκB. In order to test these hypotheses, reporter plasmids containing NFκB binding sites linked to the Interleukin 2 (IL-2) receptor α-chain promoter were constructed. SOK-1 activated IL-2 receptor a-chain expression from these constructs, indicating that SOK-1 activates NFκB. In addition, transfection of SOK-1 causes an increase in the binding of a nuclear protein to an oligonucleocide containing a consensus NFκB binding site.

A kinase inactive mutant of SOK-1 was constructed by changing the invariant lysine in the ATP binding site to an arginine. This kinase inactive mutant suppresses nuclear protein binding to the oligonucleotide containing the NFκB consensus binding site. Transcription from the NFκB reporter plasmid is also inhibited by the mutant protein. The kinase inactive mutant thus serves as a dominant inhibitor of activation of NFκB. Inhibitors of NFκB have not heretofore been identified, although they have been sought extensively, since it is believed that inhibition or stimulation of NFκB in inflammatory and autoimmune diseases, as well as cancer or viral infection, may be palliative or curative. Verma et al., Genes & Development 9:2723 (1995).

SOK-1 and Cell Cycle Arrest

Experiments were performed to investigate the role of SOK-1 in the induction of cell cycle arrest, which occurs in many types of cells following oxidant stress. In these experiments, NIH3T3 cells on coverslips were synchronized in G₀ by serum withdrawal. After twenty-four hours, less than 1% of the cells continued to cycle. Arrested cells were released with 10% calf serum, and were microinjected in early G₁ phase with the pCMV5 vector alone, or pCMV5 containing the gene encoding M2 epitope-tagged SOK-1. Entry into S phase was determined by monitoring BrdU (0.1 mM) incorporation. After microinjection of the pCMV5 vector alone, over 90% of cells entered S phase. In contrast, after injection of pCMV5-SOK-1, less than 5% of cells entered S phase. Injection of a kinase inactive mutant of SOK-1 also induced cell cycle arrest (<5% of cells in S phase).

Since both SOK-1 and the kinase inactive mutant were effective in maintaining cells in G₁, the non-catalytic carboxy terminal region of the kinase might be mediating cell cycle arrest. To test this hypothesis, pCMV5 containing only the non-catalytic region (nucleotides 858 to 1278, encoding amino acids 286 to 426) of the SOK-1 gene was injected into NIH3T3 cells. Like the constructs containing the full length SOK-1 or the kinase inactive mutant, this construct also induced G₁ arrest (<5% of cells in S phase) SOK-1 thus potently induces arrest in G₁ of the cell cycle, via a mechanism that is not dependent upon the protein's catalytic function. A fragment of the SOK-1 polypeptide of approximately forty amino acids, from amino acid 286 to 336, may be sufficient to induce cell cycle arrest.

SOK-1-mediated cell cycle arrest occurs independently of the p38 and other MAP kinases that are known to induce cell cycle arrest. The ability of SOK-1 to induce cell cycle arrest, as well as to activate NFκB, makes SOK-1 an ideal target for drug development. The ability of SOK-1 to cause cell cycle arrest also suggests that it could be used following balloon angioplasty-induced injury of blood vessels, in order to inhibit the proliferative response which accompanies such injuries and causes restenosis. SOK-1 can also be used to treat other conditions that are characterized by proliferative responses, including inflammatory responses, tumors, and conditions such as atherosclerosis.

Transgenic Animals

SOK polypeptides can also be expressed in transgenic animals. SOK transgenic animals are useful for screening for compunds that enhance or down regulate SOK expression or activity. Animals of any species, including, but not limited to, mice, rats, rabbits, guinea pigs, pigs, micropigs, goats, and non-human primates, e.g., baboons, monkeys, and chimpanzees, can be used to generate SOK expressing transgenic animals.

Various techniques known in the art can be used to introduce a SOK transgene into animals to produce the founder lines of transgenic animals. Such techniques include, but are not limited to, pronuclear microinjection (U.S. Pat. No. 4,873,191); retrovirus mediated gene transfer into germ lines (Van der Putten et al., Proc. Natl. Acad. Sci. USA, 82:6148 (1985); gene targeting into embryonic stem cells (Thompson et al., Cell, 56:313 (1989)); and electroporation of embryos (Lo, Mol. Cell Biol, 3:1803 (1983)).

The present invention provides for transgenic animals that carry the SOK transgene in all their nucleated cells, as well as animals that carry the transgene in some, but not all of their nucleated cells, i.e., mosaic animals. The transgene can be integrated as a single transgene or in concatamers, e.g., head-to-head tandems or head-to-tail tandems. For example, transgenic animals can be made in which SOK-1 is under the control of an inducible promoter. The transgene can also be selectively introduced into and/or activated in a particular cell type. Lasko et al., Proc. Natl. Acad. Sci. USA, 89:6232 (1992). The regulatory sequences required for such a cell-type specific activation will depend upon the particular cell type of interest, and will be apparent to those of skill in the art.

Vectors containing some nucleotide sequences homologous to an endogenous SOK gene can be designed for the purpose of integrating via homologous recombination into the endogenous gene and disrupting its function, i.e., making "knockout mice." The transgene also can be selectively introduced into a particular cell type, thus inactivating the endogenous SOK-1 gene in only that cell type. See Gu et al., Science, 265:103 (1984). The regulatory sequences required for such a cell-type specific inactivation will depend upon the particular cell type of interest, and will be apparent to those of skill in the art.

Once transgenic animals have been generated, the expression of the recombinant SOK gene can be assayed utilizing standard techniques. Initial screening can be accomplished by Southern blot analysis or PCR techniques to analyze animal tissues to assay whether integration of the transgene has taken place. The level of mRNA expression of the transgene in the tissues of the transgenic animals can also be assessed using techniques which include, but are not limited to, Northern blot analysis of tissue samples obtained from the animal, in situ hybridization analysis, and RT-PCR. Samples of tissues expressing SOK can also be evaluated immunocytochemically using antibodies specific for the SOK transgene product.

Therapeutic Compositions

The therapeutic compositions of the invention can be used to increase SOK expression or activity in a patient to treat a pathological condition, e.g., a condition associated with a proliferative response, such as inflammatory responses, cancer, atherosclerosis or ballon angioplasty-induced injury to blood vessels. The therapeutic compositions of the invention can also be used to treat pathological conditions associated with NKFB expression, such as transplant rejection, post ischemic injury, and the response to viral infection. These compositions can contain the polypeptides or DNAs of the invention, including SOK-1 or a fragment thereof, or a kinase inactive mutant of SOK-1. Polypeptides can be purified by methods that are known to those skilled in the art. Ausubel et al., Current Protocols in Molecular Biology, John Wiley & Sons, New York, 1995. DNAs can be administered in a manner allowing their uptake and expression by cells in vivo. DNAs can be administered to the patient by standard vectors and/or gene delivery systems. Suitable gene delivery systems include liposomes, biolistic transfer, receptor-mediated delivery systems, naked DNA and viral vectors such as herpes viruses, retroviruses, adenoviruses and adeno-associated viruses. The polypeptides and DNAs of the invention are administered with a pharmaceutically acceptable carrier, and are formulated according to procedures that are well known to those skilled in the art.

Parenteral administration, such as intravenous, subcutaneous, intramuscular or intraperitoneal delivery routes can be used to deliver the therapeutic compositions of the invention. Dosages for particular patients depend upon many factors, including the patient's size, body surface area, age, the particular substance to be administered, time and route of administration, general health and other drugs being administered concurrently. The amount of therapeutic composition to be administered to a patient can be in the range of 1 to 1000 μg/kg of body weight, e.g., 10 to 500, or 20 to 200 μg/kg of body weight. A typical dose of polypeptide or DNA to be administered to a patient is 100 μg per kilogram of body weight.

Diagnostic Applications

Anti-SOK-1 antibodies can be used to assay tissues for SOK-1; elevated SOK-1 levels may be indicative of cell stress caused, e.g., by ischemia resulting from insults such as stroke and myocardial infarction. Immunoassays using anti-SOK-1 antibody are carried out by standard techniques; e.g., the antibody can be labelled with a detectable label and contacted with a tissue sample under conditions which allow immune complexes to form. The uncomplexed labelled antibody is removed, and labelled immune complexes measured as a measure of SOK-1 in the sample. Immunoassays that can be performed using SOK-1 antibodies are well known to those skilled in the art. See e.g., Ausubel et al., Current Protocol in Molecular Biology 2: 11:2, John Wiley & Sons, 1995. Immunoassays can utilize radioactive, enzyme-based, or chemiluminescent labels.

    __________________________________________________________________________     #             SEQUENCE LISTING                                                    - -  - - (1) GENERAL INFORMATION:                                              - -    (iii) NUMBER OF SEQUENCES: 10                                           - -  - - (2) INFORMATION FOR SEQ ID NO:1:                                      - -      (i) SEQUENCE CHARACTERISTICS:                                                  (A) LENGTH: 1975 base - #pairs                                                 (B) TYPE: nucleic acid                                                         (C) STRANDEDNESS: single                                                       (D) TOPOLOGY: linear                                                  - -     (ii) MOLECULE TYPE: cDNA                                               - -     (ix) FEATURE:                                                                   (A) NAME/KEY: Coding Se - #quence                                              (B) LOCATION: 127...1404                                              - -     (xi) SEQUENCE DESCRIPTION: SEQ ID NO:1:                                - - CACCGAGCGC CCCTGGTGTC CCTCGTAGTG GACTGACGCC GCAGGGCGAG CT -             #AGCCGGCT     60                                                                  - - CCGCGCCTCT CCGCGGATCC AGACGCCTCC TGGGGCTGCT GGCGGAGGGT CT -             #GAGGCGGC    120                                                                  - - GCGGCC ATG GCT CAC CTC CGG GGA TTT GCA AAC - #CAG CAC TCT CGA GTG            168                                                                               Met Ala His Leu Arg Gly Ph - #e Ala Asn Gln His Ser Arg Val                      1         - #      5            - #      10                            - - GAC CCT GAG GAG CTC TTC ACC AAG CTC GAC CG - #C ATT GGC AAG GGC TCG           216                                                                        Asp Pro Glu Glu Leu Phe Thr Lys Leu Asp Ar - #g Ile Gly Lys Gly Ser             15                 - # 20                 - # 25                 - # 30        - - TTT GGG GAG GTC TAC AAG GGC ATC GAT AAC CA - #C ACA AAG GAG GTG GTG           264                                                                        Phe Gly Glu Val Tyr Lys Gly Ile Asp Asn Hi - #s Thr Lys Glu Val Val                             35 - #                 40 - #                 45               - - GCC ATC AAG ATC ATC GAC CTG GAG GAG GCC GA - #G GAT GAG ATC GAG GAC           312                                                                        Ala Ile Lys Ile Ile Asp Leu Glu Glu Ala Gl - #u Asp Glu Ile Glu Asp                         50     - #             55     - #             60                   - - ATC CAG CAG GAG ATC ACT GTC CTC AGT CAG TG - #C GAC AGC CCC TAC ATC           360                                                                        Ile Gln Gln Glu Ile Thr Val Leu Ser Gln Cy - #s Asp Ser Pro Tyr Ile                     65         - #         70         - #         75                       - - ACC CGC TAC TTT GGC TCC TAC CTA AAG AGC AC - #C AAG CTA TGG ATC ATC           408                                                                        Thr Arg Tyr Phe Gly Ser Tyr Leu Lys Ser Th - #r Lys Leu Trp Ile Ile                 80             - #     85             - #     90                           - - ATG GAG TAC CTG GGC GGC GGC TCA GCA CTG GA - #C TTG CTT AAA CCA GGT           456                                                                        Met Glu Tyr Leu Gly Gly Gly Ser Ala Leu As - #p Leu Leu Lys Pro Gly             95                 - #100                 - #105                 - #110        - - CCC CTG GAG GAG ACA TAC ATT GCC ACG ATC CT - #G CGG GAG ATT CTG AAG           504                                                                        Pro Leu Glu Glu Thr Tyr Ile Ala Thr Ile Le - #u Arg Glu Ile Leu Lys                            115  - #               120  - #               125               - - GGC CTG GAT TAT CTG CAC TCC GAA CGC AAG AT - #C CAC CGA GAC ATC AAA           552                                                                        Gly Leu Asp Tyr Leu His Ser Glu Arg Lys Il - #e His Arg Asp Ile Lys                        130      - #           135      - #           140                   - - GCT GCC AAC GTG CTA CTC TCG GAG CAG GGT GA - #C GTG AAG CTG GCG GAC           600                                                                        Ala Ala Asn Val Leu Leu Ser Glu Gln Gly As - #p Val Lys Leu Ala Asp                    145          - #       150          - #       155                       - - TTT GGG GTA GCA GGG CAG CTC ACA GAC ACG CA - #G ATT AAG AGG AAC ACA           648                                                                        Phe Gly Val Ala Gly Gln Leu Thr Asp Thr Gl - #n Ile Lys Arg Asn Thr                160              - #   165              - #   170                           - - TTC GTG GGC ACC CCC TTC TGG ATG GCA CCT GA - #G GTC ATC AAG CAG TCG           696                                                                        Phe Val Gly Thr Pro Phe Trp Met Ala Pro Gl - #u Val Ile Lys Gln Ser            175                 1 - #80                 1 - #85                 1 -       #90                                                                               - - GCC TAC GAC TTC AAG GCT GAC ATC TGG TCC CT - #G GGC ATC ACA GCC         ATC      744                                                                     Ala Tyr Asp Phe Lys Ala Asp Ile Trp Ser Le - #u Gly Ile Thr Ala Ile                           195  - #               200  - #               205               - - GAG CTG GCC AAG GGG GAG CCT CCA AAC TCT GA - #C CTC CAC CCC ATG CGC           792                                                                        Glu Leu Ala Lys Gly Glu Pro Pro Asn Ser As - #p Leu His Pro Met Arg                        210      - #           215      - #           220                   - - GTC CTG TTC CTG ATT CCC AAG AAC AGC CCA CC - #C ACA CTG GAG GGC CAG           840                                                                        Val Leu Phe Leu Ile Pro Lys Asn Ser Pro Pr - #o Thr Leu Glu Gly Gln                    225          - #       230          - #       235                       - - CAC AGC AAG CCC TTC AAG GAG TTC GTG GAG GC - #C TGC CTC AAC AAA GAC           888                                                                        His Ser Lys Pro Phe Lys Glu Phe Val Glu Al - #a Cys Leu Asn Lys Asp                240              - #   245              - #   250                           - - CCC CGA TTC CGG CCC ACG GCC AAG GAG CTC CT - #G AAG CAC AAG TTC ATC           936                                                                        Pro Arg Phe Arg Pro Thr Ala Lys Glu Leu Le - #u Lys His Lys Phe Ile            255                 2 - #60                 2 - #65                 2 -       #70                                                                               - - ACA CGC TAC ACC AAG AAG ACC TCC TTC CTC AC - #G GAG CTC ATC GAC         CGC      984                                                                     Thr Arg Tyr Thr Lys Lys Thr Ser Phe Leu Th - #r Glu Leu Ile Asp Arg                           275  - #               280  - #               285               - - TAT AAG CGC TGG AAG TCA GAG GGG CAT GGC GA - #G GAG TCC AGC TCT GAG          1032                                                                        Tyr Lys Arg Trp Lys Ser Glu Gly His Gly Gl - #u Glu Ser Ser Ser Glu                        290      - #           295      - #           300                   - - GAC TCT GAC ATT GAT GGC GAG GCG GAG GAC GG - #G GAG CAG GGC CCC ATC          1080                                                                        Asp Ser Asp Ile Asp Gly Glu Ala Glu Asp Gl - #y Glu Gln Gly Pro Ile                    305          - #       310          - #       315                       - - TGG ACG TTC CCC CCT ACC ATC CGG CCG AGT CC - #A CAC AGC AAG CTT CAC          1128                                                                        Trp Thr Phe Pro Pro Thr Ile Arg Pro Ser Pr - #o His Ser Lys Leu His                320              - #   325              - #   330                           - - AAG GGG ACG GCC CTG CAC AGT TCA CAG AAG CC - #T GCG GAC GCC GTC AAG          1176                                                                        Lys Gly Thr Ala Leu His Ser Ser Gln Lys Pr - #o Ala Asp Ala Val Lys            335                 3 - #40                 3 - #45                 3 -       #50                                                                               - - AGG CAG CCG AGG TCC CAG TGC CTG TCC ACG CT - #G GTC CGG CCC GTC         TTC     1224                                                                     Arg Gln Pro Arg Ser Gln Cys Leu Ser Thr Le - #u Val Arg Pro Val Phe                           355  - #               360  - #               365               - - GGA GAG CTC AAA GAG AAG CAC AAG CAG AGC GG - #C GGG AGC GTG GGT GCG          1272                                                                        Gly Glu Leu Lys Glu Lys His Lys Gln Ser Gl - #y Gly Ser Val Gly Ala                        370      - #           375      - #           380                   - - CTG GAG GAG CTG GAG AAC GCC TTC AGC CTG GC - #C GAG GAG TCC TGC CCC          1320                                                                        Leu Glu Glu Leu Glu Asn Ala Phe Ser Leu Al - #a Glu Glu Ser Cys Pro                    385          - #       390          - #       395                       - - GGC ATC TCA GAC AAG CTG ATG GTG CAC CTG GT - #G GAG CGA GTG CAG AGG          1368                                                                        Gly Ile Ser Asp Lys Leu Met Val His Leu Va - #l Glu Arg Val Gln Arg                400              - #   405              - #   410                           - - TTT TCA CAC AAC AGA AAC CAC CTG ACA TCC AC - #C CGC TGAAGCGCAC           TGCTGT   1420                                                                    Phe Ser His Asn Arg Asn His Leu Thr Ser Th - #r Arg                            415                 4 - #20                 4 - #25                             - - TCAGATAGGG GACGGAAGGT CGTTTGTTTT TGTTCTGAGC TCCATAAGAA CT -             #GTGCTGAC   1480                                                                  - - TTGGAAGGTG CCCTGTGCTA TGTCGTGCCT GCAGGGACAC GTCGGATCCC GT -             #GGGCCTCA   1540                                                                  - - CATGCCAGGT CACCAGGTCA CCGTCTCCTT CCACCCCTGC AGTGTGCTGT TG -             #TGCACGTC   1600                                                                  - - AGGACGCTGT TCTCTATGCC ACTGCCTCCT CCCTCTCCTG GCCCAGCAGT AT -             #TGCTCACG   1660                                                                  - - GGGGCTCCAG CCGCCGGCGT GGCCCTCATG AGCTACGCCT GGGTCTTCTG CA -             #GACTCATG   1720                                                                  - - CAGCCCTATG GCCGCTCAGA CCAAGGCGCA GAGCAACTAT CAGGGCATGC TC -             #TGCCTCCT   1780                                                                  - - CCTCCCATTG AGGTGGGGAG AGGCAACAGG GCAGCCCCCA GAGGAGTGTC CT -             #GGCCGCTG   1840                                                                  - - TCTCCCGGGC CCATGATGGC CATAGATTTG CCTTGTGGTG TTCCATCAGG TA -             #CTGTGTCT   1900                                                                  - - GCTCATAAGT ACTTGTGTCA TCCAGAATGT TTTGTTTTTT AAGAAAATTG AA -             #TTACTTGT   1960                                                                  - - TTCCTGAAAA AAAAA              - #                  - #                       - #  1975                                                                   - -  - - (2) INFORMATION FOR SEQ ID NO:2:                                      - -      (i) SEQUENCE CHARACTERISTICS:                                                  (A) LENGTH: 426 amino - #acids                                                 (B) TYPE: amino acid                                                           (D) TOPOLOGY: linear                                                  - -     (ii) MOLECULE TYPE: protein                                            - -      (v) FRAGMENT TYPE: internal                                           - -     (xi) SEQUENCE DESCRIPTION: SEQ ID NO:2:                                - - Met Ala His Leu Arg Gly Phe Ala Asn Gln Hi - #s Ser Arg Val Asp Pro         1               5 - #                 10 - #                 15               - - Glu Glu Leu Phe Thr Lys Leu Asp Arg Ile Gl - #y Lys Gly Ser Phe Gly                    20     - #             25     - #             30                   - - Glu Val Tyr Lys Gly Ile Asp Asn His Thr Ly - #s Glu Val Val Ala Ile                35         - #         40         - #         45                       - - Lys Ile Ile Asp Leu Glu Glu Ala Glu Asp Gl - #u Ile Glu Asp Ile Gln            50             - #     55             - #     60                           - - Gln Glu Ile Thr Val Leu Ser Gln Cys Asp Se - #r Pro Tyr Ile Thr Arg        65                 - # 70                 - # 75                 - # 80        - - Tyr Phe Gly Ser Tyr Leu Lys Ser Thr Lys Le - #u Trp Ile Ile Met Glu                        85 - #                 90 - #                 95               - - Tyr Leu Gly Gly Gly Ser Ala Leu Asp Leu Le - #u Lys Pro Gly Pro Leu                   100      - #           105      - #           110                   - - Glu Glu Thr Tyr Ile Ala Thr Ile Leu Arg Gl - #u Ile Leu Lys Gly Leu               115          - #       120          - #       125                       - - Asp Tyr Leu His Ser Glu Arg Lys Ile His Ar - #g Asp Ile Lys Ala Ala           130              - #   135              - #   140                           - - Asn Val Leu Leu Ser Glu Gln Gly Asp Val Ly - #s Leu Ala Asp Phe Gly       145                 1 - #50                 1 - #55                 1 -       #60                                                                               - - Val Ala Gly Gln Leu Thr Asp Thr Gln Ile Ly - #s Arg Asn Thr Phe         Val                                                                                              165  - #               170  - #               175              - - Gly Thr Pro Phe Trp Met Ala Pro Glu Val Il - #e Lys Gln Ser Ala Tyr                   180      - #           185      - #           190                   - - Asp Phe Lys Ala Asp Ile Trp Ser Leu Gly Il - #e Thr Ala Ile Glu Leu               195          - #       200          - #       205                       - - Ala Lys Gly Glu Pro Pro Asn Ser Asp Leu Hi - #s Pro Met Arg Val Leu           210              - #   215              - #   220                           - - Phe Leu Ile Pro Lys Asn Ser Pro Pro Thr Le - #u Glu Gly Gln His Ser       225                 2 - #30                 2 - #35                 2 -       #40                                                                               - - Lys Pro Phe Lys Glu Phe Val Glu Ala Cys Le - #u Asn Lys Asp Pro         Arg                                                                                              245  - #               250  - #               255              - - Phe Arg Pro Thr Ala Lys Glu Leu Leu Lys Hi - #s Lys Phe Ile Thr Arg                   260      - #           265      - #           270                   - - Tyr Thr Lys Lys Thr Ser Phe Leu Thr Glu Le - #u Ile Asp Arg Tyr Lys               275          - #       280          - #       285                       - - Arg Trp Lys Ser Glu Gly His Gly Glu Glu Se - #r Ser Ser Glu Asp Ser           290              - #   295              - #   300                           - - Asp Ile Asp Gly Glu Ala Glu Asp Gly Glu Gl - #n Gly Pro Ile Trp Thr       305                 3 - #10                 3 - #15                 3 -       #20                                                                               - - Phe Pro Pro Thr Ile Arg Pro Ser Pro His Se - #r Lys Leu His Lys         Gly                                                                                              325  - #               330  - #               335              - - Thr Ala Leu His Ser Ser Gln Lys Pro Ala As - #p Ala Val Lys Arg Gln                   340      - #           345      - #           350                   - - Pro Arg Ser Gln Cys Leu Ser Thr Leu Val Ar - #g Pro Val Phe Gly Glu               355          - #       360          - #       365                       - - Leu Lys Glu Lys His Lys Gln Ser Gly Gly Se - #r Val Gly Ala Leu Glu           370              - #   375              - #   380                           - - Glu Leu Glu Asn Ala Phe Ser Leu Ala Glu Gl - #u Ser Cys Pro Gly Ile       385                 3 - #90                 3 - #95                 4 -       #00                                                                               - - Ser Asp Lys Leu Met Val His Leu Val Glu Ar - #g Val Gln Arg Phe         Ser                                                                                              405  - #               410  - #               415              - - His Asn Arg Asn His Leu Thr Ser Thr Arg                                               420      - #           425                                          - -  - - (2) INFORMATION FOR SEQ ID NO:3:                                      - -      (i) SEQUENCE CHARACTERISTICS:                                                  (A) LENGTH: 268 amino - #acids                                                 (B) TYPE: amino acid                                                           (D) TOPOLOGY: linear                                                  - -     (ii) MOLECULE TYPE: protein                                            - -     (xi) SEQUENCE DESCRIPTION: SEQ ID NO:3:                                - - Pro Lys Lys Lys Tyr Thr Arg Phe Glu Lys Il - #e Gly Gln Gly Ala Ser         1               5 - #                 10 - #                 15               - - Gly Thr Val Tyr Thr Ala Met Asp Val Ala Th - #r Gly Gln Glu Val Ala                    20     - #             25     - #             30                   - - Ile Lys Gln Met Asn Leu Gln Gln Gln Pro Ly - #s Lys Glu Leu Ile Ile                35         - #         40         - #         45                       - - Asn Glu Ile Leu Val Met Arg Glu Asn Lys As - #n Pro Asn Ile Val Asn            50             - #     55             - #     60                           - - Tyr Leu Asp Ser Tyr Leu Val Gly Asp Glu Le - #u Trp Val Val Met Glu        65                 - # 70                 - # 75                 - # 80        - - Tyr Leu Ala Gly Gly Ser Leu Thr Asp Val Va - #l Thr Glu Thr Cys Met                        85 - #                 90 - #                 95               - - Asp Glu Gly Gln Ile Ala Ala Val Cys Arg Gl - #u Cys Leu Gln Ala Leu                   100      - #           105      - #           110                   - - Glu Phe Leu His Ser Asn Gln Val Ile His Ar - #g Asp Ile Lys Ser Asp               115          - #       120          - #       125                       - - Asn Ile Leu Leu Gly Met Asp Gly Ser Val Ly - #s Leu Thr Asp Phe Gly           130              - #   135              - #   140                           - - Phe Cys Ala Gln Ile Thr Pro Glu Gln Ser Ly - #s Arg Ser Thr Met Val       145                 1 - #50                 1 - #55                 1 -       #60                                                                               - - Gly Thr Pro Tyr Trp Met Ala Pro Glu Val Va - #l Thr Arg Lys Ala         Tyr                                                                                              165  - #               170  - #               175              - - Gly Pro Lys Val Asp Ile Trp Ser Leu Gly Il - #e Met Ala Ile Glu Met                   180      - #           185      - #           190                   - - Ile Glu Gly Glu Pro Pro Tyr Leu Asn Glu As - #n Pro Leu Arg Ala Leu               195          - #       200          - #       205                       - - Tyr Leu Ile Ala Thr Asn Gly Thr Pro Glu Le - #u Gln Asn Pro Glu Lys           210              - #   215              - #   220                           - - Leu Ser Ala Ile Phe Arg Asp Phe Leu Asn Ar - #g Cys Leu Glu Met Asp       225                 2 - #30                 2 - #35                 2 -       #40                                                                               - - Val Glu Lys Arg Gly Ser Ala Lys Glu Leu Le - #u Gln His Gln Phe         Leu                                                                                              245  - #               250  - #               255              - - Lys Ile Ala Lys Pro Leu Ser Ser Leu Thr Pr - #o Leu                                   260      - #           265                                          - -  - - (2) INFORMATION FOR SEQ ID NO:4:                                      - -      (i) SEQUENCE CHARACTERISTICS:                                                  (A) LENGTH: 271 amino - #acids                                                 (B) TYPE: amino acid                                                           (D) TOPOLOGY: linear                                                  - -     (ii) MOLECULE TYPE: protein                                            - -     (xi) SEQUENCE DESCRIPTION: SEQ ID NO:4:                                - - Pro Ser Thr Lys Tyr Ala Asn Leu Val Lys Il - #e Gly Gln Gly Ala Ser         1               5 - #                 10 - #                 15               - - Gly Gly Val Tyr Thr Ala Tyr Glu Ile Gly Th - #r Asn Val Ser Val Ala                    20     - #             25     - #             30                   - - Ile Lys Gln Met Asn Leu Glu Lys Gln Pro Ly - #s Lys Glu Leu Ile Ile                35         - #         40         - #         45                       - - Asn Glu Ile Leu Val Met Lys Gly Ser Lys Hi - #s Pro Asn Ile Val Asn            50             - #     55             - #     60                           - - Phe Ile Asp Ser Tyr Val Leu Lys Gly Asp Le - #u Trp Val Ile Met Glu        65                 - # 70                 - # 75                 - # 80        - - Tyr Met Glu Gly Gly Ser Leu Thr Asp Val Va - #l Thr His Cys Ile Leu                        85 - #                 90 - #                 95               - - Thr Glu Gly Gln Ile Gly Ala Val Cys Arg Gl - #u Thr Leu Ser Gly Leu                   100      - #           105      - #           110                   - - Glu Phe Leu His Ser Lys Gly Val Leu His Ar - #g Asp Ile Lys Ser Asp               115          - #       120          - #       125                       - - Asn Ile Leu Leu Ser Met Glu Gly Asp Ile Ly - #s Leu Thr Asp Phe Gly           130              - #   135              - #   140                           - - Phe Cys Ala Gln Ile Asn Glu Leu Asn Ile Ly - #s Arg Thr Thr Met Val       145                 1 - #50                 1 - #55                 1 -       #60                                                                               - - Gly Thr Pro Tyr Trp Met Ala Pro Glu Val Va - #l Ser Arg Lys Glu         Tyr                                                                                              165  - #               170  - #               175              - - Gly Pro Lys Val Asp Ile Trp Ser Leu Gly Il - #e Met Ile Ile Glu Met                   180      - #           185      - #           190                   - - Ile Glu Gly Glu Pro Pro Tyr Leu Asn Glu Th - #r Pro Leu Arg Ala Leu               195          - #       200          - #       205                       - - Tyr Leu Ile Ala Thr Asn Gly Thr Pro Lys Le - #u Lys Glu Pro Glu Asn           210              - #   215              - #   220                           - - Leu Ser Ser Ser Leu Lys Lys Phe Leu Asp Tr - #p Cys Leu Cys Val Glu       225                 2 - #30                 2 - #35                 2 -       #40                                                                               - - Pro Glu Asp Arg Ala Ser Ala Thr Glu Leu Le - #u His Asp Glu Tyr         Ile                                                                                              245  - #               250  - #               255              - - Thr Glu Ile Ala Glu Ala Asn Ser Ser Leu Al - #a Pro Leu Val Lys                       260      - #           265      - #           270                   - -  - - (2) INFORMATION FOR SEQ ID NO:5:                                      - -      (i) SEQUENCE CHARACTERISTICS:                                                  (A) LENGTH: 270 amino - #acids                                                 (B) TYPE: amino acid                                                           (D) TOPOLOGY: linear                                                  - -     (ii) MOLECULE TYPE: protein                                            - -     (xi) SEQUENCE DESCRIPTION: SEQ ID NO:5:                                - - Pro Glu Glu Val Phe Asp Val Leu Glu Lys Le - #u Gly Glu Gly Ser Tyr         1               5 - #                 10 - #                 15               - - Gly Ser Val Tyr Lys Ala Ile His Lys Glu Th - #r Gly Gln Ile Val Ala                    20     - #             25     - #             30                   - - Ile Lys Gln Val Asx Val Glu Ser Asp Leu Gl - #n Glu Ile Ile Lys Glu                35         - #         40         - #         45                       - - Ile Ser Ile Met Gln Gln Cys Asp Ser Pro Hi - #s Val Val Lys Tyr Tyr            50             - #     55             - #     60                           - - Gly Ser Tyr Phe Lys Asn Thr Asp Leu Trp Il - #e Val Met Glu Tyr Cys        65                 - # 70                 - # 75                 - # 80        - - Gly Ala Gly Ser Val Ser Asp Ile Ile Arg Le - #u Arg Asn Lys Thr Leu                        85 - #                 90 - #                 95               - - Thr Glu Asp Glu Ile Ala Thr Ile Leu Gln Se - #r Thr Leu Lys Gly Leu                   100      - #           105      - #           110                   - - Glu Tyr Leu His Phe Met Arg Lys Ile His Ar - #g Asp Ile Lys Ala Gly               115          - #       120          - #       125                       - - Asn Ile Leu Leu Asn Thr Glu Gly His Ala Ly - #s Leu Ala Asp Phe Gly           130              - #   135              - #   140                           - - Val Ala Gly Gln Leu Thr Asp Thr Met Ala Ly - #s Arg Asn Thr Val Ile       145                 1 - #50                 1 - #55                 1 -       #60                                                                               - - Gly Thr Pro Phe Trp Met Ala Pro Glu Val Il - #e Gln Glu Ile Gly         Tyr                                                                                              165  - #               170  - #               175              - - Asn Cys Val Ala Asp Ile Trp Ser Leu Gly Il - #e Thr Ala Ile Glu Met                   180      - #           185      - #           190                   - - Ala Glu Gly Lys Arg Pro Tyr Ala Asp Ile Hi - #s Pro Met Arg Ala Ile               195          - #       200          - #       205                       - - Phe Met Ile Pro Thr Asn Pro Pro Pro Thr Ph - #e Arg Lys Pro Glu Leu           210              - #   215              - #   220                           - - Trp Ser Asp Asn Phe Thr Asp Phe Val Lys Gl - #n Cys Leu Val Lys Ser       225                 2 - #30                 2 - #35                 2 -       #40                                                                               - - Pro Glu Gln Arg Ala Thr Ala Thr Gln Leu Le - #u Gln His Pro Phe         Val                                                                                              245  - #               250  - #               255              - - Arg Ser Ala Lys Gly Val Ser Ile Leu Arg As - #p Leu Ile Asn                           260      - #           265      - #           270                   - -  - - (2) INFORMATION FOR SEQ ID NO:6:                                      - -      (i) SEQUENCE CHARACTERISTICS:                                                  (A) LENGTH: 272 amino - #acids                                                 (B) TYPE: amino acid                                                           (D) TOPOLOGY: linear                                                  - -     (ii) MOLECULE TYPE: protein                                            - -     (xi) SEQUENCE DESCRIPTION: SEQ ID NO:6:                                - - Pro Ser Lys Leu Tyr Ser Ile Gln Ser Cys Il - #e Gly Arg Gly Asn Phe         1               5 - #                 10 - #                 15               - - Gly Asp Val Tyr Lys Ala Val Asp Arg Val Th - #r Gln Glu Ile Val Ala                    20     - #             25     - #             30                   - - Ile Lys Val Val Asn Leu Glu His Ser Asp Gl - #u Asp Ile Glu Leu Leu                35         - #         40         - #         45                       - - Ala Gln Glu Ile Phe Phe Leu Ala Glu Leu Ly - #s Ser Pro Leu Ile Thr            50             - #     55             - #     60                           - - Asn Tyr Ile Ala Thr Met Leu Glu Asp Val Se - #r Met Trp Ile Val Met        65                 - # 70                 - # 75                 - # 80        - - Glu Tyr Cys Gly Gly Gly Ser Cys Ser Asp Le - #u Leu Lys Arg Ser Tyr                        85 - #                 90 - #                 95               - - Val Asn Gly Leu Pro Glu Glu Lys Val Ser Ph - #e Ile Ile His Glu Val                   100      - #           105      - #           110                   - - Thr Leu Gly Leu Lys Tyr Leu His Glu Gln Ar - #g Lys Ile His Arg Asp               115          - #       120          - #       125                       - - Ile Lys Ala Ala Asn Ile Leu Ile Asn Glu Gl - #u Gly Met Val Lys Leu           130              - #   135              - #   140                           - - Gly Asp Phe Gly Val Ser Gly His Ile Arg Se - #r Thr Leu Lys Arg Asp       145                 1 - #50                 1 - #55                 1 -       #60                                                                               - - Thr Phe Val Gly Thr Pro Tyr Trp Met Ala Pr - #o Glu Val Val Cys         Cys                                                                                              165  - #               170  - #               175              - - Glu Val Asp Gly Tyr Asn Glu Lys Ala Asp Il - #e Trp Ser Leu Gly Ile                   180      - #           185      - #           190                   - - Thr Thr Tyr Glu Leu Leu Lys Gly Leu Pro Pr - #o Leu Ser Lys Tyr Asp               195          - #       200          - #       205                       - - Pro Met Lys Val Met Thr Asn Leu Pro Lys Ar - #g Lys Pro Pro Lys Leu           210              - #   215              - #   220                           - - Gln Gly Pro Phe Ser Asp Ala Ala Lys Asp Ph - #e Val Ala Gly Cys Leu       225                 2 - #30                 2 - #35                 2 -       #40                                                                               - - Val Lys Thr Pro Ala Asp Arg Pro Ser Ala Ty - #r Asn Leu Leu Ser         Phe                                                                                              245  - #               250  - #               255              - - Glu Phe Val Lys Asn Ile Thr Ile Thr Asn Le - #u Lys Ser Asp Val Asp                   260      - #           265      - #           270                   - -  - - (2) INFORMATION FOR SEQ ID NO:7:                                      - -      (i) SEQUENCE CHARACTERISTICS:                                                  (A) LENGTH: 276 amino - #acids                                                 (B) TYPE: amino acid                                                           (D) TOPOLOGY: linear                                                  - -     (ii) MOLECULE TYPE: protein                                            - -     (xi) SEQUENCE DESCRIPTION: SEQ ID NO:7:                                - - Pro Arg Asp Arg Phe Glu Leu Leu Gln Arg Va - #l Gly Ala Gly Thr Tyr         1               5 - #                 10 - #                 15               - - Gly Asp Val Tyr Lys Ala Arg Asp Thr Val Th - #r Ser Glu Leu Ala Ala                    20     - #             25     - #             30                   - - Val Lys Ile Val Lys Leu Asp Pro Gly Asp As - #p Ile Ser Ser Leu Gln                35         - #         40         - #         45                       - - Gln Glu Ile Thr Ile Leu Arg Glu Cys Arg Hi - #s Pro Asn Val Val Ala            50             - #     55             - #     60                           - - Tyr Ile Gly Ser Tyr Leu Arg Asn Asp Arg Il - #e Trp Ile Cys Met Glu        65                 - # 70                 - # 75                 - # 80        - - Phe Cys Gly Gly Gly Ser Leu Gln Glu Ile Ty - #r His Ala Thr Gly Pro                        85 - #                 90 - #                 95               - - Leu Glu Glu Arg Gln Ile Ala Tyr Val Cys Ar - #g Glu Arg Leu Lys Gly                   100      - #           105      - #           110                   - - Leu His His Leu His Ser Gln Gly Lys Ile Hi - #s Arg Asp Ile Lys Gly               115          - #       120          - #       125                       - - Ala Asn Leu Leu Leu Thr Leu Gln Gly Asp Va - #l Lys Leu Ala Asp Phe           130              - #   135              - #   140                           - - Gly Val Ser Gly Glu Leu Thr Ala Ser Val Al - #a Lys Arg Arg Ser Phe       145                 1 - #50                 1 - #55                 1 -       #60                                                                               - - Ile Gly Thr Pro Tyr Trp Met Ala Pro Glu Va - #l Ala Ala Val Glu         Arg                                                                                              165  - #               170  - #               175              - - Lys Gly Gly Tyr Asn Glu Leu Cys Asp Val Tr - #p Ala Leu Gly Ile Thr                   180      - #           185      - #           190                   - - Ala Ile Glu Leu Gly Glu Leu Gln Pro Pro Le - #u Phe His Leu His Pro               195          - #       200          - #       205                       - - Met Arg Ala Leu Met Leu Met Ser Lys Ser Se - #r Phe Gln Pro Pro Lys           210              - #   215              - #   220                           - - Leu Arg Asp Lys Thr Arg Trp Thr Gln Asn Ph - #e His His Phe Leu Lys       225                 2 - #30                 2 - #35                 2 -       #40                                                                               - - Leu Ala Leu Thr Lys Asn Pro Lys Lys Arg Pr - #o Thr Ala Glu Lys         Leu                                                                                              245  - #               250  - #               255              - - Leu Gln His Pro Phe Thr Thr Gln Gln Leu Pr - #o Arg Ala Leu Leu Thr                   260      - #           265      - #           270                   - - Gln Leu Leu Asp                                                                   275                                                                     - -  - - (2) INFORMATION FOR SEQ ID NO:8:                                      - -      (i) SEQUENCE CHARACTERISTICS:                                                  (A) LENGTH: 20 base - #pairs                                                   (B) TYPE: nucleic acid                                                         (C) STRANDEDNESS: single                                                       (D) TOPOLOGY: linear                                                  - -     (ii) MOLECULE TYPE:  Degenerate primer                                 - -     (ix) FEATURE:                                                                   (B) LOCATION: 3...3                                                            (D) OTHER INFORMATION: - #where R at position 3 is A or G                      (B) LOCATION: 4...4                                                            (D) OTHER INFORMATION: - #where Y at position 4 is C or T,                          but not - #U                                                              (B) LOCATION: 6...6                                                            (D) OTHER INFORMATION: - #where N at position 6 is Inosine                     (B) LOCATION: 12...12                                                          (D) OTHER INFORMATION: - #where N at position 12 is Inosine                    (B) LOCATION: 15...15                                                          (D) OTHER INFORMATION: - #where N at position 15 is Inosine                    (B) LOCATION: 18...18                                                          (D) OTHER INFORMATION: - #where R at position 18 is A or G            - -     (xi) SEQUENCE DESCRIPTION: SEQ ID NO:8:                                - - GARYTNATGG CNGTNAARCA            - #                  - #                       - # 20                                                                    - -  - - (2) INFORMATION FOR SEQ ID NO:9:                                      - -      (i) SEQUENCE CHARACTERISTICS:                                                  (A) LENGTH: 23 base - #pairs                                                   (B) TYPE: nucleic acid                                                         (C) STRANDEDNESS: single                                                       (D) TOPOLOGY: linear                                                  - -     (ii) MOLECULE TYPE: Degenerate primer                                  - -     (ix) FEATURE:                                                                   (B) LOCATION: 3...3                                                            (D) OTHER INFORMATION: - #where N at position 3 is Inosine                     (B) LOCATION: 6...6                                                            (D) OTHER INFORMATION: - #where N at position 6 is Inosine                     (B) LOCATION: 9...9                                                            (D) OTHER INFORMATION: - #where Y at position 9 is C or T,                          but not - #U                                                              (B) LOCATION: 12...12                                                          (D) OTHER INFORMATION: - #where N at position 12 is Inosine                    (B) LOCATION: 15...15                                                          (D) OTHER INFORMATION: - #where R at position 15 is A or G                     (B) LOCATION: 18...18                                                          (D) OTHER INFORMATION: - #where N at position 18 is Inosine                    (B) LOCATION: 20...20                                                          (D) OTHER INFORMATION: - #where K at position 20 is G or T,                         but not - #U                                                              (B) LOCATION: 21...21                                                          (D) OTHER INFORMATION: - #where R at position 21 is A or G            - -     (xi) SEQUENCE DESCRIPTION: SEQ ID NO:9:                                - - TTNGCNCCYT TNATRTCNCK RTG           - #                  - #                     23                                                                       - -  - - (2) INFORMATION FOR SEQ ID NO:10:                                     - -      (i) SEQUENCE CHARACTERISTICS:                                                  (A) LENGTH: 10 base - #pairs                                                   (B) TYPE: nucleic acid                                                         (C) STRANDEDNESS: single                                                       (D) TOPOLOGY: linear                                                  - -     (ii) MOLECULE TYPE: Kozak sequence                                     - -     (xi) SEQUENCE DESCRIPTION: SEQ ID NO:10:                               - - GCGGCCATGG                - #                  - #                       - #        10                                                                  __________________________________________________________________________ 

What is claimed is:
 1. An isolated nucleic acid molecule encoding Ste20 oxidant stress response kinase (SOK) polypeptide, said nucleic acid molecule having the ability to hybridize at 68° C. in 5×SSC, 5×Denhardt's solution, and 1.0% SDS followed by washing in 0.2×SSC and 0.1% SDS at room temperature to either strand of the coding region of the nucleotide sequence depicted in SEQ ID NO:1, said polypeptide having the ability to induce cell cycle arrest; and said polypeptide being activated by oxidant stress.
 2. The nucleic acid molecule of claim 1, wherein said nucleic acid molecule is a cDNA.
 3. The nucleic acid molecule of claim 1, wherein said nucleic acid molecule is a genomic DNA.
 4. The nucleic acid molecule of claim 1, wherein said polypeptide is human.
 5. The nucleic acid molecule of claim 1, wherein said polypeptide is able to bind to an antibody specific for an epitope within the region defined by amino acids 33-426 of SEQ ID NO:2.
 6. The nucleic acid molecule of claim 1, wherein said polypeptide has the amino acid sequence depicted in SEQ ID NO:2.
 7. The nucleic acid molecule of claim 1, wherein said polypeptide is Ste20 oxidant stress response kinase-1 (SOK-1) polypeptide.
 8. An isolated nucleic acid molecule encoding Ste20 oxidant stress response kinase-1 (SOK-1) polypeptide, said polypeptide having an apparent molecular weight of 50 kD on western blot; said polypeptide having an amino-terminal protein kinase domain and a noncatalytic carboxy-terminal domain; said polypeptide having functional activities comprising protein kinase activity; said polypeptide being activated by oxidant stress, depletion of intracellular ATP stores, or phosphorylation; and said polypeptide not being activated by epidermal growth factor (EGF), platelet-derived growth factor (PDGF), tumor necrosis factor-α (TNF-α), anisomycin, heat shock, or osmolar stress.
 9. An isolated nucleic acid molecule encoding a biologically active fragment of Ste20 oxidant stress response kinase-1 (SOK-1) polypeptide, said fragment comprising amino acids 286 to 426 of SEQ ID NO:2, said fragment having the ability to induce cell cycle arrest in a human cell.
 10. An isolated nucleic acid molecule encoding a biologically active fragment of Ste20 oxidant stress response kinase-1 (SOK-1) polypeptide, said fragment comprising amino acids 286 to 336 of SEQ ID NO:2, said fragment having the ability to induce cell cycle arrest in a human cell.
 11. An isolated nucleic acid molecule encoding a biologically active fragment of the Ste20 oxidant stress response kinase-1 (SOK-1) polypeptide, said fragment comprising the amino-terminal kinase region amino acids 1 to 285 of SEQ ID NO:2.
 12. A composition comprising the nucleic acid molecule encoding a SOK-1 polypeptide of claim
 1. 13. A composition comprising the nucleic acid molecule encoding a SOK-1 polypeptide of claim
 8. 14. A composition comprising the nucleic acid molecule encoding a SOK-1 polypeptide fragment of claim
 9. 15. A composition comprising nucleic acid molecule encoding a SOK-1 polypeptide fragment of claim
 10. 16. A composition comprising nucleic acid molecule encoding a SOK-1 polypeptide fragment of claim
 11. 17. An isolated nucleic acid molecule encoding a kinase inactive mutant of Ste20 oxidant stress response kinase-1 (SOK-1) polypeptide, said nucleic acid molecule having the ability to hybridize at 68° C. in 5×SSC, 5×Denhardt's solution, and 1.0% SDS followed by washing in 0.2×SSC and 0.1% SDS at room temperature to either strand of the coding region of the nucleotide sequence depicted in SEQ ID NO:1, said SOK-1 polypeptide having the ability to induce cell cycle arrest, and said SOK-1 polypeptide being activated by oxidant stress; said mutant of SOK-1 polypeptide having the invariant lysine within the ATP binding site is substituted or deleted, and said mutant having the ability to induce cell cycle arrest.
 18. The nucleic acid molecule of claim 17, wherein the SOK-1 polypeptide has the sequence depicted in SEQ ID NO:2 and the mutation is an arginine substitution.
 19. An expression vector comprising the nucleic acid molecule of claim
 1. 20. An expression vector comprising the nucleic acid molecule of claim
 8. 21. An expression vector comprising the nucleic acid molecule of claim
 9. 22. An expression vector comprising the nucleic acid molecule of claim
 10. 23. An expression vector comprising the nucleic acid molecule of claim
 11. 24. An expression vector comprising the nucleic acid molecule of claim
 17. 25. A host cell comprising the vector of claim
 19. 26. A host cell comprising the vector of claim
 20. 27. A host cell comprising the vector of claim
 21. 28. A host cell comprising the vector of claim
 22. 29. A host cell comprising the vector of claim
 23. 30. A host cell comprising the vector of claim
 24. 31. A method of producing an Ste20 oxidant stress response kinase-1 (SOK-1) polypeptide, said method comprising culturing the host cell of claim 25 under conditions permitting expression of SOK-1 polypeptide and isolating the expressed SOK-1 polypeptide.
 32. A method of producing an Ste20 oxidant stress response kinase-1 (SOK-1) polypeptide, said method comprising culturing the host cell of claim 26 under conditions permitting expression of SOK-1 polypeptide and isolating the expressed SOK-1 polypeptide.
 33. A method of producing an Ste20 oxidant stress response kinase-1 (SOK-1) polypeptide, said method comprising culturing the host cell of claim 27 under conditions permitting expression of SOK-1 polypeptide and isolating the expressed SOK-1 polypeptide.
 34. A method of producing an Ste20 oxidant stress response kinase-1 (SOK-1) polypeptide, said method comprising culturing the host cell of claim 28 under conditions permitting expression of SOK-1 polypeptide and isolating the expressed SOK-1 polypeptide.
 35. A method of producing an Ste20 oxidant stress response kinase-1 (SOK-1) polypeptide, said method comprising culturing the host cell of claim 29 under conditions permitting expression of SOK-1 polypeptide and isolating the expressed SOK-1 polypeptide.
 36. A method of producing an Ste20 oxidant stress response kinase-1 (SOK-1) polypeptide, said method comprising culturing the host cell of claim 30 under conditions permitting expression of SOK-1 polypeptide and isolating the expressed SOK-1 polypeptide.
 37. An isolated nucleic acid molecule comprising at least 10 consecutive nucleotides of either strand of the coding region of the nucleic acid sequence depicted in SEQ ID NO:1, said nucleic acid molecule having the ability to hybridize at 68° C. in 5×SSC, 5×Denhardt's solution, and 1.0% SDS followed by washing in 0.2×SSC and 0.1% SDS at room temperature to one of the strands of a nucleotide sequence encoding a Ste20 oxidant stress response kinase (SOK) polypeptide, said polypeptide having the ability to induce cell cycle arrest; and said polypeptide being activated by oxidant stress.
 38. The nucleic acid molecule of claim 37, wherein said nucleic acid molecule comprises at least 18 consecutive nucleotides.
 39. The nucleic acid molecule of claim 37, wherein said nucleic acid molecule comprises at least 30 consecutive nucleotides.
 40. An isolated nucleic acid molecule comprising at least 10 consecutive nucleotides of either strand of the coding region of the nucleic acid sequence depicted in SEQ ID NO:1, said nucleic acid molecule having the ability to hybridize at 68° C. in 5×SSC, 5×Denhardt's solution, and 1.0% SDS followed by washing in 0.2×SSC and 0.1% SDS at room temperature to the nucleic acid sequence depicted in SEQ ID NO:1.
 41. The nucleic acid molecule of claim 40, wherein said nucleic acid molecule comprises at least 18 consecutive nucleotides.
 42. The nucleic acid molecule of claim 40, wherein said nucleic acid molecule comprises at least 30 consecutive nucleotides.
 43. An isolated nucleic acid molecule comprising the coding region of SEQ ID NO:1, or a degenerate variant thereof.
 44. The nucleic acid molecule of claim 43, wherein said nucleic acid molecule comprises the coding region of SEQ ID NO:1. 